Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$116.83	6.336%	$124.2323	$124.23	$124.25	$124.20
Purchase #2	$208.69	8.206%	$225.8151	$225.82	$225.80	$225.80
Purchase #3	$39.40	8.371%	$42.6982	$42.70	$42.70	$42.70
Purchase #4	$128.38	11.726%	$143.4338	$143.43	$143.45	$143.40
Purchase #5	$72.41	8.757%	$78.7509	$78.75	$78.75	$78.80
Purchase #6	$11.68	7.658%	$12.5745	$12.57	$12.55	$12.60
Purchase #7	$144.29	3.217%	$148.9318	$148.93	$148.95	$148.90
7 purchase totals =	$721.68		$776.4366	$776.43	$776.45	$776.40